This invention relates generally to the pumping of wells, and more particularly concerns highly advantageous pumping apparatus characterized as solving problems associated with such pumping.
Fluid wells such as oil wells must be pumped when natural or other oil field pressure drops below certain limits. Such pumping frequently involves vertical reciprocation of so-called sucker rods connected to a pump plunger at the sub-surface pump location. For example, as the plunger moves up, a valve ball in the top of the plunger seats and lifts the fluid up into the production tubing. At the same time, a valve ball in the pump barrel or chamber opens and allows fluid from the well to enter into the barrel interior. A typical tubing pump may have a plunger diameter of 23/4 inches and is attempting to pull in fluid at a displacement rate corresponding to 5.94 square inches of area; however, the area through the standard A.P.I. seat is only 2.07 square inches. This restriction prevents maximum filling of the barrel chamber and thus a loss in pump efficiency is experienced.
On the plunger down stroke, the ball valve in the top of the plunger opens, and the valve in the barrel closes, trapping the fluid and forcing it up through the upper valve in the plunger. The orifice in the valve in the top of the plunger causes an extremely high restriction, and fluid resistance. Such high fluid resistance in turn causes the pump rods to go into compression, producing accelerated fatique and premature breakage of the rods. This resistance also shows the descent of the rods so that the strokes per minute are limited and flow of pumped fluid is also undesirably limited. Furthermore, undesirably elevated pressures are produced within the pump barrel or chamber as the weight of the rods trying to fall is supported by the trapped fluid below the plunger. Although the traveling valve in the top of the plunger is open allowing the trapped fluid to be displaced up through the plunger; the annular seat in that valve is so small that it commonly has only 20 to 22% as much square inch area as the area of the plunger. The elevated pressure also causes extra wear between the sealing surfaces of the plunger and barrel, as well as abrupt imparting of downward impacts on the tubing string, causing fatigue at the threaded coupling joints.
Additional problems with such operation include stretching and unstretching of the very long rod string during its reciprocation, which produces undesirable motion of the pump plunger, interfering with pump operation and reducing pumping efficiency. This leads to limited production from a given pump, at depth. Also, the pump orifices restrict the flow to undesired extent, limiting production. Therefore, there is great need for pumping apparatus which will overcome these practical difficulties.